Eye examinations have been widely performed for the purpose of early diagnosis of diseases which top the list of lifestyle-related diseases and causes of blindness. Tomographic eye image pickup device, such as optical coherence tomography (OCT), are useful for disease diagnosis because a state in retinal layers can be three-dimensionally observed through the device.
The retina at the back of an eye has a layered structure including a plurality of layers. Information concerning the layered structure, e.g., the thickness of each layer, is used as an objective indicator to measure the extent of a disease. In order to use such an indicator, a technique of analyzing a tomographic image of the retina to accurately determine the layered structure and identifying the kind of boundary between layers is important.
U.S. Pat. No. 7,347,548 discloses a technique of detecting two strong edges in the depth direction in a tomographic image and identifying the edge adjacent to the shallow side as a boundary corresponding to the inner limiting membrane and the edge adjacent to the deep side as a boundary corresponding to the retinal pigment epithelium. This technique focuses on that the inner limiting membrane and the retinal pigment epithelium, serving as retinal tissue, appear as strong edges in a tomographic image.
WO publication 2009034704 A1 discloses, as a technique of determining a change in layered structure, a technique of determining the presence or absence of an artifact of a blood vessel. This technique utilizes that a signal remarkably attenuates in a region under a blood vessel to provide uniform image characteristics and is intended to determine the presence or absence of an artifact on the basis of pixel values in the vicinity of the boundary of a layer.
For example, in case of vitreous cortex detachment, the vitreous cortex floats above the inner limiting membrane. According to the technique disclosed in U.S. Pat. No. 7,347,548, the vitreous cortex may be erroneously detected as the inner limiting membrane. As described above, it is difficult to accurately identify the boundaries of retinal layers according to change in the layered structure due to a disease or change in imaging region or conditions.
Furthermore, for response to not only artifacts but also a change in the layered structure, the characteristics of the retinal layers remarkably vary depending on position in the depth direction. Accordingly, the boundary of a layer cannot be accurately identified on the basis of only a state in the vicinity of the boundary of the layer as disclosed in WO publication 2009034704 A1.